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Science: Cellulose bacteria

10 June 1989

BACTERIA that ‘fix’ nitrogen from the atmosphere into nitrogen compounds
are essential for the fertility of the soil. In order to fix the nitrogen,
these bacteria need readily available sources of energy. One potential source
is cellulose. However, biologists were unsure until recently whether it
provided food for bacteria that fix atmospheric nitrogen.

Recent research by S. Leschine and his colleagues at the University
of Massachusetts at Amherst has shown that four strains of bacteria involved
in the breakdown of cellulose can fix nitrogen from the atmosphere (Science,
vol 242, p 1157). The bacteria were all anaerobic; that is, they did not
require oxygen to function.

The researchers isolated the four strains from forest soil and freshwater
mud and grew the bacteria in two liquid media, both of which lacked nitrogen
compounds but included cellulose. The team exposed one culture to gaseous
nitrogen and the other to an inert gas, argon. They found that much of the
cellulose in the liquid exposed to nitrogen had gone after a period between
seven and 14 days. The amount of cellulose exposed to argon remained unchanged.

Leschine’s group also showed that the bacteria contained nitrogenase,
an enzyme involved in fixing atmospheric nitrogen.

Many soils are rich in cellulose but contain few nitrogen compounds
– for example, peat soils or municipal or agricultural waste sites. The
researchers point out that it would be possible to make such soils much
more fertile by adding to them these bacteria.